Kinetics and mechanism of formation of binary and ternary complexes of nickel(II) and nickel(II)-2- aminomethylbenzimidazole with 3-nitrosalicylate and <i>cis</i>- (ammine )(3-nitrosalicylato) bis (ethylenediamine)cobalt(III) : Evidence for the slow interconversion of the structural isomers of the ternary complexes

Abstract

The kinetics of complex formation of 3-nitrosalicylate(NSAH^-) and <em>cis</em>-(en)₂(NH₃)(3-nitrosalicylato)cobalt(III) with Ni(OH₂)₆²⁺ and [Ni(AMB)(OH₂)₄]²⁺ (AMB = 2- aminomethylbenzimidazole) have been investigated. The formation of the ternary complexes [Ni(AMB)(NSA)(OH₂)₂] and [(en)₂(NH₃)Co{NSA=Ni(AMB)(OH₂)₂} ]³⁺ displayed biphasic kinetics due to the slow and reversible structural isomerisation (<em>trans</em>- (diaqua) species &Ucirc; <em>cis</em>-( diaqua) species). The formation of [Ni(NSA)(OH₂)₄] is chelation-controlled. The isomerisation of the ternary complexes is presumed to involve Ni- N (benzimidazolyl-N) bond cleavage and rearrangement of the intermediate.